It is generally understood that ceramides present within the intercellular lipid lamellae of the stratum corneum play an important role in the production and maintenance of the water permeability barrier of the skin. Ceramides, or substances closely related to them, have been disclosed as components of skin care compositions. In particular, Kao Corporation in GB 2 178 312 and GB 2 213 723 disclose the use of natural ceramides extracted from skin in topical products. Also, Unilever in EP 97059 disclose -linoleoyl ceramides and emphasize their role in the water barrier function of the skin.
It is believed that one of the causes of dry skin and ageing skin is a reduction in the amount of lipid contained within these intercellular lipid lamellae. It is therefore desirable to be able successfully to replace these depleted lipids via the topical route.
One of the problems associated with the topical application of skin and hair care products containing ceramides or their synthetic analogues, is devising a suitable method for delivering them effectively to the lipid lamellae, without causing permanent disruption of the stratum corneum. It is accordingly apparent that permanently disrupted stratum corneum is unable to retain molecules of this sort, as they are simply washed out again when the stratum corneum (skin) is contacted with water.
This problem has not successfully been solved to date.
Kao Corporation have reported in GB 2 178 312, EP 227 994 and EP 282 816, that co-surfactants such as glyceryl ethers assist synthetic ceramide, to penetrate into the stratum corneum. However, these co-surfactants tend to disrupt the stratum corneum, so that when penetration occurs allowing the synthetic ceramide access to the lipid lamellae, there is nothing to prevent them being washed out again on contact with water.
Certain phosphorylated and sulphated derivatives of ceramides have been prepared in the course of scientific investigation of natural metabolism or to make liposomes for drug delivery.
Thus Karpyshev, Bushnev et al Bioorg Khim 5(2) 238 (1979) and 5(9) 1381 (1979) describe preparation of phosphorylated derivatives of ceramides by routes which entail the use of protective groups which are eventually removed.
Japanese published application JP-A-89/299265 discloses the preparation of ceramide sulphates to be used for liposome production.